Hypochlorous acid is an oxidant and biocide that is produced by the human body's natural immune system to fight infection. Hypochlorous acid is generated as the final step of the Oxidative Burst Pathway, with large quantities of hypochlorous acid being released into the phagocytic vesicles to destroy the invading microorganisms. It is considered that hypochlorous acid exerts its biocidal effect by attacking the surface and plasma membrane proteins, impairing transport of solutes and the salt balance of bacterial cells (Pieterson et al., Water SA, 22(1):43-48 (1996)). Escherichia coli exposed to hypochlorous acid lose viability in less than 100 ms due to inactivation of many vital systems. (Fair et al., 40 J. Am. Water Works Assoc. 1051-61 (1940)). Hypochlorous acid at 2.6 ppm caused 100% growth inhibition of E. coli in dilute bacterial suspensions in about 5 minutes. (Chesney et al., 178 J. Bacteria 2131-2135 (1996)). According to Chemistry of Water Treatment (2nd Edition), S. D. Faust and O. M. Aly (1998), 100% kill in 5 minutes requires only 0.08 ppm for A. aerogenes, 0.06 ppm for S. typhosa, 0.05 ppm for S. dysenteriae, and 0.03 ppm for E. coli. 
Although hypochlorous acid is biocidal for microorganisms, it is not significantly toxic to human or animal cells, at least partly because human and animal cells have extensive, highly effective defense mechanisms known as the Antioxidant Defense System (ADS).
Hypohalous acid has a wide range of applications where it is important to control microbial contamination, such as for the care and management of wounds, disinfecting hard surfaces such as medical or dental equipment, food safety and processing, water treatment, as well as other industrial and agricultural applications.
One limitation associated with solutions of hypochlorous acid is their stability, which has limited much of the commercial use to those situations where the solution can be made on site for relatively immediate use. Existing alternatives include Dakin's solution for wound care, which is a diluted sodium hypochlorite solution (0.5%) prepared by mixing sodium hypochlorite (5.25%), sodium bicarbonate/carbonate (1%), and clean tap water. However, Dakin's solution has a high pH, and thus causes pain and burning in wound treatment along with rashes, itching, swelling, hives, and/or blisters. Further, Dakin's solution is unstable and unsuited for clinical use at lower pH's (<8.5). Another alternative is the Microcyn™ solution. While Microcyn has a 2 year shelf life, it suffers from a limited level of available free chlorine (AFC) of about 80 ppm (pH of 7.4), and lower percent of hypochlorous acid, which may limit its biocidal effectiveness. EcaFlo™ is available for hard surface disinfection. This solution contains equimolar amounts of hypochlorite and hypochlorous acid in addition to high sodium chloride content. The pH of the solution is around 7.5 and the solution has an AFC content of approximately 460 ppm. The solution has a relatively short shelf life of 30 days.
There is an unmet need for a hypohalous acid solution that has a high AFC content, has sufficient stability and/or other properties required to be commercially useful in medical and other commercial settings, and is not irritating or harmful to humans. The claimed invention meets these and other objectives.